scholarly journals Bayesian estimation of the lethargy coefficient for probabilistic fatigue life model

2017 ◽  
Vol 5 (2) ◽  
pp. 191-197 ◽  
Author(s):  
Jaehyeok Doh ◽  
Jongsoo Lee
Keyword(s):  
Fatigue Life ◽  
Sampling Method ◽  
Bayesian Updating ◽  
Unknown Parameters ◽  
Life Data ◽  
Mcmc Sampling ◽  
Fatigue Model ◽  
Relative Stress ◽  
Life Model ◽  
Static Tensile

Abstract In this study, a model for probabilistic fatigue life that is based on the Zhurkov model is suggested using stochastically and statistically estimated lethargy coefficients. The fatigue life model was derived using the Zhurkov life model, and it was deterministically validated using real fatigue life data as a reference. For this process, firstly, a lethargy coefficient that is related to the failure of materials must be obtained with rupture time and stress from a quasi-static tensile test. These experiments are performed using HS40R steel. However, the lethargy coefficient has discrepancies due to the inherent uncertainty and the variation of material properties in the experiments. The Bayesian approach was employed for estimating the lethargy coefficient of the fatigue life model using the Markov Chain Monte Carlo (MCMC) sampling method and considering its uncertainties. Once the samples are obtained, one can proceed to the posterior predictive inference of the fatigue life. This life model was shown to be reasonable when compared with experimental fatigue life data. As a result, predicted fatigue life was observed to significantly decrease in accordance with increasing relative stress conditions. Highlights Zhurkov fatigue life model is deterministically validated with experiments. Prediction of the S-N curve using Zhurkov fatigue model and lethargy coefficients. Lethargy coefficients of Zhurkov fatigue model are estimated by Bayesian updating. Bayesian updating is useful for quantifying the uncertainty of unknown parameters.

Probabilistic Analyses of Industrial Gas Turbine Durability

1993 ◽  
Author(s):  
R. Craig McClung ◽  
Henry L. Bernstein ◽  
Janet P. Buckingham ◽  
James M. Allen ◽  
George L. Touchton
Keyword(s):  
Fatigue Life ◽  
Crack Length ◽  
Gas Turbine ◽  
Large Data ◽  
Thermal Mechanical Fatigue ◽  
Fatigue Model ◽  
Life Model ◽  
Standard Normal ◽  
Input Variables ◽  
Industrial Gas Turbine

Probabilistic analyses of component durability have been developed for first stage buckets and nozzles in General Electric MS7001B and MS7001E industrial gas turbine engines. The analyses illustrate two different approaches to the development of probabilistic durability algorithms. The bucket algorithm is built around an existing thermal-mechanical fatigue life model which predicts average fatigue life as a function of local strains, dwell times, and constants in the fatigue model derived from laboratory testing. The fatigue model is linked to a fast probability integration method which calculates the uncertainty or variability in the response variable (life or damage) resulting from uncertainties or variabilities in the physical input variables. The nozzle cracking algorithm, in contrast, is built around a large data base of crack length sums for each vane on seven different nozzles from the field. The crack length sums on nozzles with similar numbers of fired starts were described with standard normal distributions. Extreme value distributions were then calculated analytically to describe the crack length sums on the single most heavily cracked vane per nozzle for different probability levels.

Damage Identification for Masonry Materials Based on Bayesian Inference

2013 ◽  
Vol 405-408 ◽  
pp. 2498-2502
Author(s):  
Xiang Ping Fu ◽  
Bin Peng ◽  
Zheng Ji
Keyword(s):  
Monte Carlo ◽  
Markov Chain ◽  
Sampling Method ◽  
Damage Identification ◽  
Dynamic Test ◽  
Finite Element Models ◽  
Masonry Structures ◽  
Dynamic Tests ◽  
Bayesian Inferences ◽  
Mcmc Sampling

The basic frequency of masonry specimens can be obtained by dynamic tests with ambient or artificial excitation. The elastic modulus of masonry structures, as well as the damage factors, can then be determined by training their finite element models and make the calculated frequencies agree with the measured ones. Using 530 groups of dynamic test data, the damage factors of four masonry specimens were identified. The Bayesian inferences of the highly diverse measured results were conducted through a Markov Chain Monte Carlo (MCMC) sampling method, and the location of the damage was identified. The methodology was applicable, and can be used in the damage identification for other materials or structures.

Fatigue Strength of Ribbon Bonds

2010 ◽  
Author(s):  
S. M. Bresney ◽  
A. Saigal
Keyword(s):  
Thermal Expansion ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Manufacturing Process ◽  
Electronic Components ◽  
Mechanical Method ◽  
Temperature Changes ◽  
Life Model ◽  
Short Span ◽  
Different Levels

Ribbon or wire bonding is a common manufacturing process used in the microelectronic industry to make interconnections between electronic components. This process is used because it can make up for misalignment and inconsistent spacing between the components due to tolerance stack ups. In addition, since the ribbons are not rigid they will flex and absorb any stresses that develop when the components expand and contract in the field due to temperature changes. This paper investigates the use of a mechanical method to exercise ribbons in this fashion until they failed. Ribbons of a constant profile but different sizes were exercised at different levels of stress to develop a fatigue life model. It is found that ribbons exercised only a small percentage of their overall span survive exponentially longer than the same ribbons exercised at a higher percentage of their overall span. In addition, at short span lengths relative to the thickness, the ribbon becomes less ‘thread like’ and more stiff. The model developed in this study can be used for designing ribbon size and shape based upon expected thermal expansion cycling and necessary life or reliability.

Fatigue Life Prediction of Vortex Reducer Based on Stress Gradient

2018 ◽  
Author(s):  
Yanbin Luo ◽  
Yanrong Wang ◽  
Bo Zhong ◽  
Jiazhe Zhao ◽  
Xiaojie Zhang
Keyword(s):  
Fatigue Life ◽  
Size Effect ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Notched Specimens ◽  
Life Model ◽  
The Mean

The effects of stress gradient and size effect on fatigue life are investigated based on the distributions of stress at notch root of the notched specimens of GH4169 alloy. The relationship between the life of the notched specimens and the smooth specimens is correlated by introducing the stress gradient effect factor, and a new life model of predicting the notched specimens based on the Walker modification for the mean stress effect is established. In order to improve the prediction precision of life model with the equation parameters having a definite physical significance, the relationships among fatigue parameters, monotonic ultimate tensile strength and reduction of area are established. Three-dimensional elastic finite element (FE) analysis of a vortex reducer is carried out to obtain the data of stress and strain for predicting its life. The results show that there is a high-stress gradient at the edge of the air holes of the vortex reducer, and it is thus a dangerous point for fatigue crack initiation. The prediction result of the vortex reducer is more reasonable if the mean stress, stress gradient and size effect are considered comprehensively. The developed life model can reflect the effects of many factors well, especially the stress concentration. The life of the notched specimens predicted by this model give a high estimation precision, and the prediction life data mainly fall into the scatter band of factor 2.

Contact fatigue model and life prediction of the compound motion curve-face gear pair

2020 ◽  
Vol 44 (3) ◽  
pp. 440-451
Author(s):  
Chao Lin ◽  
Peilu Li ◽  
Chunjiang He ◽  
Qingkun Xing
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Contact Fatigue ◽  
Tooth Surface ◽  
Gear Pair ◽  
Face Gear ◽  
Fatigue Model ◽  
Contact Fatigue Life ◽  
Five Axis ◽  
Curve Face

Different from the common face gear pair fixed rotation motion between intersecting axes, the compound transmission of the curve-face gear is a new motion form, which can convert rotational motion into rotation and movement motion. To solve the contact fatigue life problem of this new motion form gear pair, a new contact fatigue life calculation method of the compound transmission curve-face gear pair was proposed. Based on the space gear engagement principle and the fracture mechanics theory, the theoretical contact fatigue model of the curve-face gear composite transmission was established. Considering that the contact load for every tooth is time-varying in the half-period of the curve-face gear, the contact fatigue life stage of the curve-face gear was divided into crack initiation and crack growth, and the crack growth fatigue life for each tooth was calculated using the finite element method. The curve-face gear pair was processed in the five-axis NC machining center and the compound transmission experiment platform of the curve-face gear was set up to measure the tooth surface dynamic contact stress, and the overall life of the curve-face gear was predicted. The comparison analysis between theoretical and experimental results verified the correctness of the theoretical contact fatigue calculation model.

scholarly journals Structural component fatigue analysis of a hydrogenerator rotor

DYNA ◽  
2020 ◽  
Vol 87 (214) ◽  
pp. 155-164
Author(s):  
Gonzalo Fernando Casanova Garcia ◽  
Andres Felipe Cardona Gutierrez ◽  
Carlos Alberto Mantilla Viveros
Keyword(s):  
Fatigue Life ◽  
Multiaxial Fatigue ◽  
Finite Element Models ◽  
Electrical Parameters ◽  
Stress History ◽  
Ground Failure ◽  
Gravity And Magnetic ◽  
Fatigue Model ◽  
One Year ◽  
Pulling Force

This paper presents a fatigue life calculation for the pole, the rotor rim, and the rotor spoke of a 100 MW hydro-generator. Mechanical and electrical parameters during unit start, with the hydro-generator working at several power levels, and during a load rejection from 100 MW were measured. The measured loads together with centrifugal force, gravity, and magnetic pulling force were included in finite element models to quantify stresses. Also, stresses produced during over-speed, phase-to-ground failure, and phase-to-phase failure were evaluated. A stress history for each element was obtained by fitting the calculated stresses, with the power generation history collected hourly during one year of operation of the machine. Fatigue life calculation was performed by using the stress history along with the Wang-Brown multiaxial fatigue model.

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